Arguments:

in

The B-format signal, an array: [w, x, y, z]

angle

The distortion angle, in radians. -pi/2 to pi/2

mul

Output will be multiplied by this value.

add

This value will be added to the output.

Discussion:

Focus is a normalised dominance variant, specified in terms of a distortion angle. Positive values of angle maintain gain at [0, 0], while reducing at [pi, 0]. Negative values do the inverse. The default, 0, results in no change.

In contrast with zoom, gain is maintained at 0dB in the direction of distortion.